1. Field of the Invention
This invention relates to an inspection electrode unit for printed wiring board, inspection apparatus comprising the inspection electrode unit and a process for inspecting a printed wiring board using the same.
2. Discussion of Background
With respect to printed wiring boards having fabricated therein integrated circuits and the like, in generally, it is necessary to inspect the electric characteristics of the printed wiring boards before fabricating integrated circuits and the like in order to check whether the wiring patterns of the printed wiring boards have the desired performance. Heretofore, in order to carry out the inspection of printed wiring boards, there has been used, basically, an inspection electrode unit of the individually responding type in which inspection electrodes are arranged correspondingly to the patterns of electrodes to be inspected of a printed wiring board and in which the inspection electrodes are electrically connected to the inspection circuits of a tester by means of wirings. Alternatively, a so-called universal type inspection electrode unit in which inspection electrodes are placed at the standard grids arranged crosswise has been used in combination with a connector for connecting the electrodes to be inspected of a printed wiring board to the inspection electrodes of the inspection electrode unit.
Recently, in the field of a printed wiring board, there has been a tendency that the degree of integration of element and the pattern density are being heightened more and more, and as a result, the inspection electrode density of an inspection electrode unit is also being heightened. However, the inspection electrode unit of the individually responding type is required to have inspection electrodes of a pattern corresponding to the electrodes to be inspected of a printed wiring board, and hence, it is finally required that inspection electrodes must be formed at a density as high as in electrodes to be inspected using spring probes though said inspection electrode unit has an advantage that the individually responding type enables the inspection circuit to be utilized more effectively than the universal type. Accordingly, there has been the problem that it is difficult to produce the inspection electrode unit and the cost becomes very high.
In the case of the universal type inspection electrode unit, the distance between adjacent electrodes in pairs to the inspection circuit of a tester is constant, and hence, it is sufficient that a part of the electrodes to be inspected are electrically connected to the inspection electrodes of the unit nearest to the electrodes to be inspected. However, another part of the electrodes to be inspected is often required to be electrically connected to inspection electrodes placed in considerably distant positions. This is because the density of electrodes to be inspected is considerably higher than that of the inspection electrodes. As a result, it becomes necessary to increase the wiring density in connector; however, there is a limit in heightening the density. In fact, there remain many inspection electrodes which cannot effectively be used, and hence, there is the problem that they are inferior in efficiency and have useless parts.
As discussed above, it is difficult for conventional inspection electrode units for printed wiring board to respond well to the desired heightening of the density of electrodes to be inspected. As a result, the construction of inspection electrode unit becomes complicated and it is difficult to sufficiently heighten the density of wiring pattern in a connector for achieving electrical connection. Hence, it is impossible to carry out highly reliable inspection.